1. Field of the Invention
This invention relates to machine tools having a rotating spindle, for example milling machines.
2. Description of the Prior Art
In machine tools having a rotating spindle the cutting stress may be reduced suddenly from a high value to zero, then resume its initial value just as suddenly. This happens in particular when working on a surface to be dressed by one of its edges, as is inevitable at the beginning of each pass; the same phenomenon is found when working with straight-toothed or slightly spiral-fluted cutters as with cutters of so-called constant profile form in which one tooth attacks the material each time with its entire width.
This phenomenon, termed interrupted cutting, makes the gear wheels of the kinematic chain clatter in their play, which produces an unpleasant noise and tends to cause the cutting edges of the tools to break at the moment of attack; they are immobilised for a time, even an extremely short time, and then receive something like a hammer blow when the play in the kinematic chain is violently taken up.
It is known that a fly-wheel arranged on the spindle of the machine or on a shaft located upstream and connected without play to the said spindle provides an effective remedy for this disadvantage.
However for such a fly-wheel to be effective it must be very large and in fact it is often mounted on the rear part of the spindle and in the open air; this arrangement excludes its use on universal cutters in which the spindle must be capable of orientation in every direction. For the same reason of effectiveness it is sometimes located on a control shaft rotating faster than the spindle. The transmission to the latter must then be without appreciable play. In addition, if the fly-wheel is useful for cutters of relatively large diameter, for which the spindle rotates slowly, it may be harmful and even dangerous when the spindle rotates rapidly. The energy necessary to bring it up to speed is then too great as is that lost to bring it to a standstill; moreover, for reasons of safety it must be possible to immobilise a spindle virtually instantaneously in the event of an accident.